1. Field of the Invention
The present invention relates to a liquid crystal display device of matrix type, and more particularly to a liquid crystal display device in which non-display areas are light shielded by opaque metal electrodes.
2. Related Background Art
The surface-stabilized ferroelectric liquid crystal device proposed by Clark and Lagerwall (hereinafter called SSFLC; see the Japanese Laid-Open Patent Application No. 56-107216 or the U.S. Pat. No. 4,367,924) is a bistable ferroelectric liquid crystal (FLC) device in which the ferroelectric liquid crystal can assume two stable oriented states.
In an SSFLC device of matrix type in which a ferroelectric liquid crystal layer is sandwiched between a pair of electrode layers of mutually crossing stripe-patterns, a pixel area defined by the crossing area of the mutually opposed electrodes can be switched to one of the aforementioned two states by the application of a voltage from an external driving circuit. However, there may result following drawbacks in the non-display areas outside said crossing areas or pixels areas.
Firstly, because of the bistability of SSFLC, the liquid crystal present in such non-pixel areas also assume two oriented states, which appear as mixed black and white areas when observed through polarizers attached on both faces of the display device. For this reason a liquid crystal display (LCD) panel of a large area contains areas showing unintended display states, thereby giving a granular appearance to the entire display panel.
Secondly, there is known a phenomenon called "interpixel switching". As shown in FIG. 5A, if a pixel G is in the "black" state, an adjacent interpixel area K gradually changes to black. However, after the pixel is inverted to white by an external voltage application, the interpixel area, which is not subjected to said voltage application, remains in the black state, thus inducing an apparent after image in a large-area FLC panel, remaining for a period of several seconds to more than several tens of seconds.
The transparent stripe electrodes in ordinary LCD devices are composed of indium oxide, which however shows an increased wiring resistance particularly in a large-area LCD panel, with the reduction in width of the wirings. Such increased resistance results in a signal delay, proportional to the product of the capacitance of the liquid crystal layer and the wiring resistance, and such signal delay is being avoided by a reduction in resistance, achieved by forming a metal electrode on the upper end of each stripe electrode.
Such metal electrode may be utilized for light shielding in the inter-pixel areas, by an electrode patterning technology for use in the liquid crystal shutter array, as disclosed for example in the Japanese Patent Publication Sho 63-38689. If this technology is applied to the stripe electrode patterns, the mutually opposed metal electrodes are to be shaped as indicated by 342 respectively in FIGS. 3A and 3B.
However, if the stripe electrode patterns are mutually positioned according to this method in a large-area SSFLC panel, the superposed area 43 of the upper and lower metal electrodes 42, as shown in FIG. 4, occupies a considerable portion.
Such metal electrode is generally deposited with a thickness of 500-5,000 .ANG. A on the transparent electrode, and the probability of short-circuiting of the upper and lower metal electrodes increases drastically at said superposed area 43, as the gap therebetween is as small as 1.5 .mu.m particularly in case of a ferroelectric liquid crystal display panel.